This invention relates to phase comparison monopulse radar, and more particularly to a phase stable, adjustable phase slope limiter.
In certain types of monopulse tracking systems, such as the AN/TPN-19 Pulse Acquisition Radar, angle error information is contained in the phase of the signal processed in the two or three channels of the monopulse receiver. To provide gain normalization over the dynamic range, the signal is typically processed through limiting IF amplifiers. To assure that these limiting amplifiers do not add angle errors of their own to the processed signal, the phase shift through the limiter should remain constant over the entire dynamic range which is 65 db for the AN/TPN-19. An alternative is to allow the phase to vary in a prescribed manner with signal level and then match the sum and difference channels, or preferably normalizing to a constant phase where testing and aligning is simplified. The best phase versus level performance is obtained when the limiter bandwidth is very wise, i.e., when as many harmonics of the input signal as possible are passed, thus minimizing reflections and recombination, in uncontrolled phase, of these high frequency components. In the AN/TPN-19 radar, for example, the limiter presented here at 74 MHz provides excellent performance with typically less than 1.degree. peak variation over the 65 db limiting dynamic range.